Dwaynes69BB

at the same time the oil pan gasket is being replaced. I have a serious oil leak that I was hoping was just the oil pan gasket but I'm afraid it may be the main seal. It's making a disgusting mess underneath (coating everything). Any advise when tackling this project?

I am planing a complete engine rebuild soon but I don't think I can wait until then to correct this oil mess. :(

roger68

Yes, the rear main seal can be replaced. Sometimes the upper half comes out fairly easy and other times it's not so easy. I had one heck of a time getting the upper half out of my '68 327. The factory service manual outlines the procedure. Just to clarify, we're talking a two-piece rear main seal.

Roger

Paul L

Yes, that two-piece seal can certainly be replaced. Mitchell flat rate shows it at about a 3-hour job if you are inclined to let some else do it. The nice thing about the two-piece is that the transmission does not have to come out. C3s have some advantages.

Gator81

Just a coupla thots to add to the above:

I've done this procedure, but not on a BB chevy... On the engines I've done, it requires the pan be completely out of the way, so you can loosen the main bearing caps enough to get just a hair of clearance for removing/inserting the seal. Not a bad time to take a look at your bearings and see how bad you're tempting fate on the ol' motor... also a good time to put on a new oil pump, especially if you decide to make those bearings hold on for awhile...

Also, there's a handy little tool made by Lisle, sold at Pep Boys and some other autoparts stores, that helps get the new seal in place without damage. It's a little cable with a hook on it. You feed the cable over the crank, hook onto the new seal, and pull it (rather than pushing it) into place.

I've read the procedure... can't remember right now if it was in the GM shop manual or the Haynes, but it was one or the other.

Good luck! :seeya

Dwaynes69BB

Thanx Gator,
Great advice about the pump & bearings. Somehow I just knew that this would turn into more than a simple pan gasket project. seems to always happen like that huh. :rolleyes:
Last month a rear wheel bearing job turned into a complete front and rear suspension rebuild. :D

roger68

When I did mine I did replace the oil pump and I also put in an all steel pump drive shaft, new pickup, HD stuff, etc. You need to remove the rear main cap to replace the lower half. Don't use any sort of a tool that can scratch the block or rear main cap - use something aluminum, brass, nylon, etc. I used a GM seal from the GM Perf Parts catalog - supposed to be new, improved, etc. There's a procedure for applying some sealant to prevent leaks - it came with the seal and I want to say the factory shop manual outlines the same basic thing, but I don't remember for sure. Also, I offset the seal ends a tad so they don't match up with the mating surfaces of the block/cap and I also put a tiny dab of Permatex Ultra Black on the seal ends - don't use much at all. One more thought would be to use one of the new one-piece oil pan gaskets. Fel-Pro has them for small blocks, but I'm not 100% sure they have them for big blocks, but I believe so - a very slick piece. Not sure if it was the same Lisle tool mentioned above, but I bought a Lisle tool when I was having so much grief getting the top half out. It didn't help me a bit and it struck me as something that would be helpful if you were trying to install a rope seal, but that was about it. The aluminum piece that's supposed to help get the upper half out was junk. I ended up making my own out of brass stock and that was the only way I got the top half out - I was darn near to the point of pulling the engine. Good luck and post if you need help!

Roger

Chris@VetteFinders

I replaced mine a while back by just pushing the new half of the seal in which in turn pushed the old seal around and out. Unfortunately, it appears to be leaking again.

john's '81 mouse

Roger 68 is right on target with his comments. I replaced rear seal on my small block last fall. Advice to slightly loosen ALL main bearing caps is very good advice indeed, believe it really helps in the seal removal process, the closer you move to the front of the engine, the less you have to loosen the caps, but DO loosen them all. I found that a brass punch was best to get the upper half of the seal broken loose so it could be pushed out. I used a clean old ice cream bar stick to push the seal out, after knocking it loose with the punch, worked like a charm. Also used felpro rear seal, came with a special plastic installation 'tool', (follow special instructions on where to, and where not to place special sealant) and used felpro one piece rubber pan gasket, along with installing new standard main and rod bearings, new stock oil pump, and steel oil pump drive shaft, no leaks at rear of engine!

dladd74roadster

Yes it can be done. I did mine this past weekend. You don't, however, have to loosen any of the main caps with the exception of removing the rear main. You will want to have a small piece of plastic or something else to use as a shoehorn to keep the sharp edge of the block from "shaving" the new seal as you install it. What typically happens if you don't use one is that as you are pushing it around and above the crank, the sharp mating surface for the rear main cap shaves rubber from the underside of the seal. This causes it not to seal as tightly and will eventually leak. If you use a very thin piece of plastic cut to the same thickness as the groove as the back of the seal, you will be able to protect this groove from damage as you are rotating it into place.

Hope this helps.

dl

Dwaynes69BB

John,
This is probably a stupid Question but how did you change the main bearings (esp. upper) without removing the crank?

Chris@VetteFinders

I think he is only talking about changing the rear main seal.


[Modified by Rhys, 1:11 PM 8/10/2001]

john's '81 mouse

Dwaynes69BB:

You can change main bearings with engine in the car, and the crankshaft installed, I know, because I did it on my 350. You simply loosen all main cap bolts 3 or 4 turns, then remove one cap at a time and replace that particular bearing and move on to the next. I used a spcecial tool I cut out from a piece of sturdy, yet somewhat flexible plastic, and used this tool to push out the upper main bearing once the cap is removed, if the bearing would not come out by 1st simply turning the crankshaft by hand.

My crankshaft was smooth and showed no wear or grooving, so I installed new standard bearings, used the clearance tape and retorqued the bearing cap, and then removed and read the results. I got .002 to .003 clearance with the new standard bearings, which is within acceptalble limits, so I installed the new bearings in place of the old ones which showed obvious wear. With new stock oil pump and these new bearings, oil pressure is now great.

Dwaynes69BB

I never would have thunk it was possible! :D
Good to know that can be done with engine in car..I'll check mine when the pan is off.